1. Field of the Invention
The invention relates to a heater member for a chair and a method for producing the same. More specifically, the invention relates to a heater member for a chair, wherein a plurality of conductive threads woven into a fabric as a part of constituent yarn have substantially the same length even though the dimension of the heater member as measured in the width direction varies from portion to portion, so that the temperature of the heater member can be uniformly raised not only in the width direction (that is the same direction as the course direction of the fabric), but also in the longitudinal direction (that is the same direction as the wale direction of the fabric), so as to uniformly and sufficiently warm a seat of the chair, or the like. The invention also relates to a method for producing such a heater member for a chair.
2. Description of the Related Art
A seat for a vehicle, in particular, for a passenger automobile, or the like, is known in which a heater member is attached to a rear surface of a skin material of a seat bottom, or the like, so as to warm a passenger from the down side in the wintertime, for example. A seat heater for heating a seat of a chair provided with a seatback is disclosed in Japanese Patent Application Publication No. 2008-67850 (JP-A-2008-67850), in which a heater member used in the seat is woven from and comprised of a plurality of conductive warp threads that generate heat when energized, and a plurality of non-conductive weft threads that are electrically insulated from the conductive warp threads, and the conductive warp threads are arranged more closely in a portion remote from the seatback, than in a seatback-side portion close to the seatback. In the seat heater, the conductive warp threads in the seatback-side portion that bears a larger proportion of the weight of a seated passenger than the other portion of the seat of the chair are less likely or unlikely to be largely bent and disconnected each time the passenger is seated.
As a heater used in a seat, one type of product has been developed which is formed by cutting out a heater member having a predetermined shape, from an original fabric into which conductive threads are woven as yarn constituting the fabric, and attaching the heater member to a rear surface of a skin material of the seat. In this type of product, the heater member having the predetermined shape, which is cut out from the original fabric, is used. In the meantime, a seat of a passenger automobile, or the like, is often shaped such that the width of the seat bottom or seat cushion is reduced from the front side to the back side, and the width of the seat back is reduced from the top to the bottom. In this case, the length of the conductive threads increases from the back side to the front side of the seat bottom, and increases from the top to the bottom of the seat back. In operation, the conductive threads having varying lengths are connected in parallel and are energized; therefore, the temperature of the seat bottom is less likely to increase in its front portion with which the thigh of the passenger contacts, and the temperature of the seat back is less likely to increase in its upper portion with which the shoulder and back of the passenger contact. Thus, it is difficult to sufficiently warm passenger's regions, such as the thigh, shoulder and back, which are desired to be warmed. In JP-A-2008-67850, no study has been made in terms of variations in the temperature rise due to variations in the length of the conductive threads.